Endoscopic surgery involves inserting surgical instruments through small incisions to perform a surgical procedure on the interior organs and tissues. By using these instruments in this manner, it is not necessary to create a large open incision to gain access to the organs and tissues. In this regard endoscopic surgery is regarded as minimally invasive.
Although there are many types of endoscopic surgical procedures, the present invention will be described with respect to a laparoscopic procedure conducted within a patient's abdominal cavity. Of course, the scope of the present invention is not limited to such laparoscopic procedures.
To access the internal organs and tissues and to provide adequate space for conducting the surgical procedure, the abdominal or other body wall is distended away from the tissues and organs by pressurizing the abdominal or other internal cavity. A viewing device known as a laparoscope and a light source are inserted into the abdominal cavity to allow the surgeon to view the surgical site and the surgical effects created by use of the instruments. Most present laparoscopes typically include a miniature electronic video camera by which to view the surgical site with a monitor.
The typical surgical instruments used during the laparoscopic procedure are both mechanical and electrosurgical. Mechanical laparoscopic surgical instruments include knives, snares and graspers which are attached to the ends of relatively long manipulating tools. Electrosurgical instruments generally take the form of one or more relatively long, insulated electrodes through which high frequency, high voltage electrical current is delivered to cut tissue, coagulate bleeding from the tissue or to cut and coagulate simultaneously at the surgical site.
The surgical instruments and laparoscope are inserted into the abdominal cavity through cannulas. A cannula is a tube-like device which extends through an incision formed in the abdominal wall. An interior opening in the cannula allows the surgical instruments and other accessories to pass from the exterior of the patient into the abdominal cavity. The interior opening of the cannula also includes a sealing device to prevent the escape of the pressurized gas from within the abdominal cavity.
Laparoscopic electrosurgical procedures present increased possibilities for unintended electrical burns to the patient and to the attending surgical personnel, compared to typical open electrosurgical procedures. In general, unintended burns result from the fact that the electrosurgical current flows in a path which is not intended, obvious, anticipated or consistent. Protective equipment has been devised to eliminate and avoid unintended burns in open electrosurgical procedures, and some of this protective equipment, such as a return electrode contact quality monitor, is useful and desirable during laparoscopic electrosurgical procedures. However, adequate protective equipment to guard against the causes of unintended burns during laparoscopy has not previously been available. Indeed, some of the leading causes of unintended burns during laparoscopy appear not to be fully understood or appreciated.
Practical considerations that increase the possibilities of unintended burns during laparoscopic procedures (compared to open electrosurgery) include: the requirement that high frequency, high voltage electrical current must pass through the cannula; the limitation on the observation area within the abdominal cavity to that which is illuminated; and the restriction that interaction with the tissues and organs can occur only through the instruments inserted through the cannula.
If the cannula becomes electrically charged as a result of electrical energy being transferred from the electrode to the cannula during electrosurgery, and if the cannula is the typical uninsulated metal type which is in direct contact with the abdominal wall at the insertion site, the cannula will conduct the current into the abdominal wall. A void, separation or break in the insulation of the electrosurgical electrode may allow the cannula to become unintentionally charged if the defect in the insulation is located within the length of the cannula. Additionally, even if the electrode insulation is undamaged, the relatively high frequency electrosurgical current will capacitively couple from the electrode to the closely adjacent metal cannula, thereby electrically charging the cannula. The metal cannula can also become electrically charged if the active end of the electrosurgical electrode inadvertently contacts the cannula within the abdominal cavity while electrosurgical current is delivered to the electrode.
With respect to the restricted view of the surgical site within the abdominal cavity, not only is the view limited to the area illuminated by the small light source, but the viewing perspective within the abdominal cavity is limited to a two dimensional view from the laparoscope. Without the third dimension to provide viewing perspective or depth of field, the active end of the electrode can be erroneously positioned while electrosurgical current is being delivered. A mistakenly positioned electrode can cause burns in unintended locations. Furthermore, the limited viewing area resulting from the limited illumination and camera angle may fail to reveal that some of the instruments are incorrectly positioned or that the instruments are positioned in a location which will result in inadvertent contact with the active electrode. Inadvertent contact between a metal instrument and the active electrode can electrically charge the instrument, and contact of that charged instrument with the tissue or organs can cause unintended burns.
Similarly, when the tissue or organs are held with graspers or are otherwise contacted by an instrument and electrosurgical current is applied, there is a possibility that the current return path through the held or contacted tissue will include the graspers or instruments and the surgical personnel manipulating the graspers or other instruments. The possibility of an unintentional return path through the graspers or other contacted instruments increases substantially as the tissue is severed from the patient. As the tissue is severed, the return path through the patient decreases in size and therefore increases in impedance, thereby increasing the chance of an unintended return path through the grasper and the person holding the grasper.
Furthermore, in addition to causing unintentional patient burns, contact with the active electrode may damage many present laparoscopic surgical instruments. For example, many present laparoscopes include electronic circuitry such as an IC chip within the instrument housing to provide the ability to send video images to a monitor in the operating room. Such circuitry is susceptible to electrical interference and may be irreparably damaged should the laparoscope become unintentionally charged during the minimally invasive procedure.
To address some of these risks and concerns, it has been strongly recommended that only electrically conductive (i.e., metal) cannulas be employed in laparoscopic electrosurgery. This recommendation is based on the assumption that a metal or electrically conductive cannula will harmlessly dissipate unintentional electrical charges to the abdominal wall. The size of the metal cannula and the thickness of the abdominal wall has been regarded as sufficient to safely dissipate any current without creating patient burns. By discharging the unintentional current from the cannula into the abdominal wall in this manner, the risk of unintentional burns from an electrically charged cannula is thought to be avoided. However, it has been found that when a metal cannula is directly coupled to the active electrode (such as by direct contact with the electrode tip or through insulation failure), the current discharged through the cannula can injure the abdominal wall tissue at the site where the cannula is inserted through the abdominal wall.
As an adjunct to the recommendation that only metal conductive cannulas be used, it has been recommended that plastic nonconductive cannulas and plastic nonconductive retaining devices for metal cannulas not be used. Plastic cannulas will not conduct electrical charges into the abdominal wall, thereby preventing a return path through the abdominal wall for any unintended electrical charge. Similarly, the use of plastic retention devices which insulate metal cannulas from the abdominal wall has also been discouraged. Plastic retention devices prevent the discharge of any unintended electrical charge to the abdominal wall. When the metal cannula is insulated from the abdominal wall by the plastic retention device, there is an increased possibility that the inner end of the metal cannula within the abdominal cavity might contact a tissue or organ and thereby discharge at that location causing an unintended burn. The inner end of the cannula frequently rests against interior organs is easily moved into such a position because of the flexibility of the abdominal wall. A burn from an unintentional contact of the inner end of a charged cannula with the bowel can cause a perforation of the bowel, leading to dangerous consequences.
Other recommendations for reducing unintentional burns relate to improving laparoscopic surgical technique. For instance, care should be taken to avoid unintentionally contacting the active electrode with other instruments and with tissues during the surgical procedure. Additionally, electrical energy should only be delivered to the active electrode when the position of the active electrode has been confirmed. Furthermore, the light source should be accurately positioned to illuminate all the relevant areas within the abdominal cavity.
One piece of existing equipment directed to resolving some of the concerns of unintended burns during laparoscopic electrosurgery, disclosed in U.S. Pat. No. 5,312,401 to Newton et al. for an ELECTROSURGICAL APPARATUS FOR LAPAROSCOPIC AND LIKE PROCEDURES, utilizes a shield that slides over the active electrode before it is extended into the abdominal cavity through the cannula. A monitor attached to the shield monitors the level of current coupled to the shield and disables the electrosurgical generator if an unacceptable level of current is coupled to the cannula. While this device appears to be effective in resolving problems of capacitive coupling and insulation failure when used with a metal cannula, it is not effective in resolving many of the other concerns associated with laparoscopic electrosurgery. For example, the device will not prevent the unintentional energization of other instruments not associated with the active electrode, such as mechanical graspers. Furthermore, the device is relatively expensive and presents additional issues of complexity in equipment use during surgery.
A relatively old technique suggested for use in urinary procedures is to attach a ground wire between a colonoscope and the electrosurgical generator to prevent the surgeon from burning his eye while peering through the eyepiece of the colonoscope. Such a system is not intended to prevent unintentional patient burns and will not prevent other laparoscopic instruments from being accidentally energized.
It is with respect to these and other considerations that the present invention for eliminating or reducing the possibility of unintended burns to the patient and the surgical personnel during laparoscopic electrosurgery has evolved.